Re: [PATCH v3 04/35] x86/bugs: Restructure mds mitigation

Brendan Jackman
2025-02-10T16:14:03Z

On Wed, 8 Jan 2025 at 21:27, David Kaplan <david.kaplan@amd.com> wrote:
> +/*
> + * Speculation Vulnerability Handling
> + *
> + * Each vulnerability is handled with the following functions:
> + * <vuln>_select_mitigation() -- Selects a mitigation to use. This should
> + * take into account all relevant command line
> + * options.
> + * <vuln>_update_mitigation() -- This is called after all vulnerabilities have
> + * selected a mitigation, in case the selection
> + * may want to change based on other choices
> + * made. This function is optional.
> + * <vuln>_apply_mitigation() -- Enable the selected mitigation.

Maybe also worth calling out cpu_bugs_smt_update() here?

> +/* Return TRUE if any VERW-based mitigation is enabled. */
> +static bool __init verw_mitigation_enabled(void)
> +{
> + return (mds_mitigation != MDS_MITIGATION_OFF ||
> + (taa_mitigation != TAA_MITIGATION_OFF &&
> + taa_mitigation != TAA_MITIGATION_TSX_DISABLED) ||
> + mmio_mitigation != MMIO_MITIGATION_OFF ||
> + rfds_mitigation != RFDS_MITIGATION_OFF);
> +}

Since you defined such nice terminology above, why not use it here and
say verw_mitigation_selected()?

(Obviously if the alternative was a respin for this trivial issue
alone I would prefer to merge with the current name!)

> +static void __init mds_update_mitigation(void)
> +{
> + if (!boot_cpu_has_bug(X86_BUG_MDS) || cpu_mitigations_off())
> + return;
> +
> + /* If TAA, MMIO, or RFDS are being mitigated, MDS gets mitigated too. */
> + if (verw_mitigation_enabled()) {
> + if (boot_cpu_has(X86_FEATURE_MD_CLEAR))
> + mds_mitigation = MDS_MITIGATION_FULL;
> + else
> + mds_mitigation = MDS_MITIGATION_VMWERV;
> + }

This is changing what the user will see in sysfs. This seems good to
me, but it would be worth calling it out in the commit log I think.